1. Field of the Invention
The present invention relates to an ink-jet print head and an ink-jet recording apparatus adapted for printing by ejecting an ink droplet from a nozzle aperture, and more particularly, to an ink-jet print head and ink-jet recording apparatus which employ an ink, such as an aqueous ink, which is prone to form bubbles hard to penetrate.
2. Description of the Related Art
Conventionally, ink-jet recording apparatuses have been known which are adapted to record characters or images on a receiving medium by means of an ink-jet print head having a plurality of nozzles for ink ejection. In such ink-jet recording apparatuses, the ink-jet print head is assembled with a head holder as directing its nozzles toward the receiving medium, whereas the head holder is mounted to a carriage to scan along a direction orthogonal to a direction in which the receiving medium is conveyed.
One example of such an ink-jet print head is shown in an exploded perspective view of FIG. 14. As seen in FIG. 14, a piezoelectric ceramic plate 121 is formed with a plurality of grooves 122 extended in parallel with one another and separated from one another by sidewalls 123. Each of the grooves 122 has one longitudinal end thereof extended to one end face of the piezoelectric ceramic plate 121. The other longitudinal end of each groove is not extended to the other end face of the piezoelectric ceramic and, therefore, the groove is progressively decreased in depth toward the other end thereof. In each groove 122, the opposite side walls 123 are formed with electrodes 124 for drive voltage application on their surface portions on an open side, the electrode extending along the longitudinal length of the side wall.
An ink chamber plate 126 is bonded to the piezoelectric ceramic plate 121 on the open side of the grooves 122, defining a common ink chamber 125 communicated with the shallowed ends of the grooves 122.
Fixed on the ink chamber plate 126 is a flow-path base plate 128 which seals one side of the common ink chamber 125 and has a communication hole 127 communicated with an ink supply path for supplying ink to the common ink chamber 125.
The flow-path base plate is provided with an ink reservoir 129 for supplying the ink to the common ink chamber 125.
A nozzle plate 130 is bonded to an end face of a unified body of the piezoelectric ceramic plate 121 and the ink chamber plate 126, into which face the grooves 122 open. The nozzle plate 130 is formed with nozzle apertures 131 in correspondence with the grooves 122.
In the ink-jet print head thus arranged, the ink is filled in the grooves 122 via the communication hole 127. When a predetermined driving electric field is applied to the side walls 123 on the opposite sides of a given groove 122 via the electrodes 124, the side walls 123 are transformed so that the volume of the given groove 122 is varied. This causes the ink in the groove 122 to be ejected through the nozzle aperture 131.
Such an ink-jet print head has a problem of ink jet failure which, for example, is caused by foreign substances contained in the ink. In this connection, a mesh filter 132 is disposed in the communication hole 127 at an end thereof adjoining the common ink chamber 125 in order to prevent the foreign substances and the like contained in the ink from entering the common ink chamber 125. Such a filter 132 also serves to apply a back pressure to the grooves 122.
Unfortunately, the ink reservoir of the conventional ink-jet print head includes a region where the ink flow tends to stagnate. For instance, the ink flow introduced into the ink reservoir becomes stagnant at a corner portion thereof or the like, where air bubbles accumulate. The accumulation of the air bubbles in such a region reduces the ink volume in the ink reservoir so that a shortage of ink supply to the ink chamber results. Particularly when the ink, such as an aqueous ink, which is prone to form bubbles of low penetration is used, the dwell of the air bubbles is pronounced.
Such air bubbles remaining in the ink reservoir are generally removed by sucking from the nozzle apertures or by performing a so-called cleaning operation. Unfortunately, the cleaning operation cannot fully remove the air bubbles from the region where the ink flow stagnates.
Thus, the ink-jet print head incapable of removing the air bubbles from the region suffering the ink flow stagnation is discarded because the remaining air bubbles are allowed to pass the filter during printing operations to be ejected along with the ink droplets so that a print failure results. As a result, the yield is decreased.
Furthermore, in a case where the ink droplets have large sizes or a large number of nozzle apertures are provided or where a large quantity of ink is ejected per unit time, the amount of air bubbles remaining in the ink reservoir is particularly increased so that the area of the ink flow path is substantially decreased. Accordingly, the shortage of ink supply to the ink chamber becomes more and more serious.
It may be contemplated to increase the flow rate of the ink by narrowing the flow path in the ink reservoir thereby purging the air bubbles from the ink reservoir. However, the size of the filter is substantially decreased, resulting in the shortage of ink supply to the common ink chamber.